The invention is applicable in mobile communication systems with either digital or analog radio paths. Analog mobile communication systems are disclosed, for example, in MPT 1327, A Signalling Standard for Trunked Private Land Mobile Radio Systems, January 1988, revised and reprinted November 1991, and MPT 1343, Performance Specification, January 1988, revised and reprinted September 1991, both issued by the Radio-communications Agency, published by the British Department of Trade and Industry. Digital mobile communication systems are disclosed, for example, in ETS 300 392-1, February 1996, Radio Equipment and Systems; Trans-European Trunked Radio (TETRA); Voice plus Data (V+D); Part 1: General network design, ETSI, 195 pages.
A radio network may comprise a plurality of exchanges, and one system often comprises a plurality of organizations with different needs concerning subscriber numbering.
In order to ensure an individual subscriber number for each subscriber in a radio network, the entire mobile communication system typically uses a common numbering domain. A radio network, particularly a PMR (Private Mobile Radio) network, is typically used by many organizations, which want to use the subscriber identifiers, e.g. numbers, in their own way.
In a fixed telephone network, subscriber numbers are assigned to users in such a way that the numbering domain is divided between different exchanges, and the subscriber of a certain exchange is assigned a subscriber number from the block of the numbering domain allocated to that exchange. In such a case, the block, or part, of the numbering domain allocated to the organizations is not necessarily continuous, but different identifiers must be assigned to subscribers located in the service areas of different exchanges. The identifiers thus show that the subscribers are located in the service areas of different exchanges.
Organizations naturally wish to be allocated a continuous block of the numbering domain irrespective of in which exchanges data of their subscribers are located. On the other hand, when the system comprises a plurality of organizations, the subscriber numbering must meet the special needs of all the organizations.
Furthermore, sometimes the clients wish that the subscriber number did not directly disclose certain information on the subscriber. Therefore the aim is to find a solution where the subscriber identifier does not directly indicate the organization to which the subscriber in question belongs or his position in that organization.
The problems with cases of the prior art where the radio network comprises a plurality of exchanges sharing the same numbering domain are the allocation of subscriber numbers to the different exchanges, and the location of the home data bases of subscribers in the different exchanges. This is problematic, because there is no applicable way of reading the location of a subscriber's home exchange or subscriber data base from the subscriber number, if subscriber numbers are not allocated exchange-specifically.
Another problem with the solutions of the prior art is that subscriber numbering in fixed telephone networks is directly dependent on the exchange. Subscriber numbers are allocated to users in such a way that the numbering domain is divided between different exchanges, and a subscriber of a certain exchange is assigned a subscriber number from the block of the numbering domain allocated to the exchange.
Furthermore, if subscriber numbering is to be arranged in such a manner that the number does not disclose anything directly (not even the subscriber's home exchange), finding the home data base of a subscriber presents a problem, when the subscriber is visiting the areas of other exchanges.
In a GSM network, home data bases are provided in home location registers HLR. A network may comprise 1 to n HLRs. Usually the HLRs are operator-specific.